This invention relates to an improvement of a dust-proof actuator having a carriage which is built in a housing and is linearly driven in the axial direction.
An example of a conventional dust-proof clean actuator has been disclosed, for instance, by Japanese Utility Patent Unexamined Publication No. Hei. 7-7837. The dust-proof clean actuator, as shown in FIG. 1, comprises: a linear guide device 101; a carriage 102 guided by the linear guide device 101; and a drive device 103 which drives the carriage in the axial direction with the aid of a ball screw. The linear guide device 101, the carriage 102 and the drive device 103 are built in a housing 100. The housing 100 has a slit in its one surface which is elongated in the direction of movement of the carriage 102. A part of the carriage 102 is protruded from the housing 100 through the slit so that a carrying table (not shown) is mounted on it. A plurality of pulleys 105 are arranged at both ends of the housing 100, and seal belts are laid on those pulleys, thus forming a movable loop. The carriage 102 is coupled to the movable loop thus formed. The movable loop closes the slit, to prevent dust such as metal powder or grease particles produced inside the housing from scattering outside.
The above-described conventional dust-proof actuator suffers from the following difficulty: In the case when the carriage 102 is moved at high speed, in the housing the air in front of the carriage as viewed in the direction of movement of the carriage 102 becomes higher in pressure than the outside air pressure, so that the air may leak out through the slit which ought to be kept closed with the seal belt 106.
Hence, in order to use the above-described dust-proof actuator, for instance, as a part carrying robot in a dust-less/clean room in which the scattering of even a considerably small quantity of extremely small dust particles is not permitted, the actuator must be modified as shown in FIG. 2. That is, the actuator is covered with a cover 110, and a discharge pump 112 is operated to discharge the air from the inside of the cover 110, to form a negative pressure therein, thereby to completely prevent the scattering of extremely small dust particles. Particularly, the use of the discharge pump 112 for forming the negative pressure in the inside of the cover 110 makes the structure of the dust-proof actuator complicated and troublesome. This is a problem.